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Gemini North Back On-sky: Dome Repairs Complete

February 18, 2014

Figure 1. Gemini North showing the crane used to lift the drive unit back into place.

Figure 2. Drive unit repair team, from left to right: 1st row - Chris Yamasaki, Steve Hardash, Jon Archambeau, Edmund Daog Sr. (Isemoto Contracting); 2nd row - Maitland Akau (Isemoto Contracting), Harlan Uehara, Rody Kawaihae, Marcel Tognetti, Markus Kissler-Patig; 3rd row - Cooper Nakayama, Keane Nakatsu, Joseph D'Amato, Clayton Ah Hee.

Figure 3. Harlan Uehara (right) supervises as the repaired drive box begins its ascent back to the dome.

Figure 4. Steve Hardash (left) and Cooper Nakayama (right) inspect the drive box after reinstallation on the Gemini North dome.

On December 27, 2013 technicians at Gemini North identified that one of the top shutter’s drive units had a critical failure with its spherical bearing system. The system, not designed for in-situ repairs, is a complex mechanism used to open and close the 22-ton shutter system via large chains, and is located within the Gemini dome shutter. To perform repairs it requires an involved process of stabilizing the shutter, releasing the drive chains, and removing the 2-ton+ drive unit. Even under ideal conditions this work would require multiple weeks of effort.

Due to this premature failure of the drive’s bearing system (which keeps the drive sprockets aligned to the drive chain) it was determined that in order to protect the shutter and telescope from potential risk, a shutdown was necessary. The shutdown was turned into a high-priority project and resources were made available to repair the drive unit -- located high on the exterior of the Gemini North dome (see Figure 1). Gemini’s staff worked collectively to assess the necessary repairs and formulate a plan to perform the work.

The process of formulating the best possible techniques and procedures to perform this work required hiring outside structural engineering consultants to work with the Gemini staff. These experts, recognized world leaders in their industry, worked closely with Gemini staff to ensure that this project was executed using best practices in safety for personnel and the facility.

Repair tasks and procedures were formulated and carefully reviewed by Gemini engineering staff and consultants, and they immediately made preparations for implementation. However, the first step, removal of the shutter drive box, was delayed from the original schedule by extreme weather that included extremely high winds. During this period, winds peaked at well over 100 miles per hour, and the removal of the unit couldn’t occur until both the wind subsided and subsequent snowfall was removed. Finally, on January 31st, the drive unit was removed and lowered by crane and repairs began inside the Gemini North facilities. The necessary repairs were performed on the unit and on February 11th conditions allowed the reinstallation of the unit. By February 15th Gemini North was ready for observations.

Throughout all of this, Gemini staff documented the procedures (including the photos used in this article) which will be used for future reference since these drive units are used in the top and bottom shutters on both Gemini North and South domes. In addition, work is underway to carefully review the existing data to monitor the unit’s operation for clues on the cause of this failure and to prevent future occurrences.

Gemini would like to thank its users and the community for their support throughout this shutter repair project and would like to acknowledge the staff (Figure 2) for their skill, dedication and safety-oriented approach to efficiently complete this project.

Report by Joseph D’Amato